This invention relates to test systems for aircraft indication switches and is particularly useful in connection with thrust reverser indication switches on turbojet powered aircraft.
Most present day turbojet aircraft employ thrust reverser mechanisms for reversing the direction of jet flow from the engines for purposes of braking the forward movement of the aircraft. Inadvertent deployment of the thrust reversers during normal flight can adversely affect the performance of the aircraft, even to the point of losing control of the aircraft. For these reasons, various indication switches are associated with different parts of the thrust reverser mechanisms for monitoring their status and warning of undesired conditions. Unfortunately, one or more of the indication switches may themselves become defective and cause an alarm that may be falsely identified as a system failure. It would be desirable, therefore, to be able to identify the occurrence of a switch failure as a switch failure and not a thrust reverser or other system failure and to identify the particular switch that failed. This would enable appropriate corrective action to be taken with a minimum negative impact to thrust reverser or other system availability.
For the foregoing reasons, there is a need for a device capable of detecting and identifying that the occurrence of a thrust reverser or other system switch failure is not indicative of an actual thrust reverser or other system failure.
One aspect of the present invention provides a built-in test system for aircraft indication switches for identifying the occurrence of a switch failure and the identity of the particular switch that failed. The test system comprises a plurality of aircraft indication switches for providing information on various aircraft functions. The test system further includes a first resistor adding network having input resistors individually connected to first contacts of different ones of the indication switches. The test system also includes a second resistor adding network having input resistors individually connected to second contacts of different ones of the indication switches. The test system additionally includes circuitry for individually coupling the outputs of the first and second resistor adding networks to an electronic control unit for the aircraft.
In another aspect of the invention, there is provided a method of testing aircraft indication switches. This method includes the step of monitoring first contacts of a group of aircraft indication switches for obtaining first indications of switch status. This method also includes the step of monitoring second contacts of the same group of aircraft indication switches for obtaining second indications of switch status. The method further includes the step of comparing the first and second indications for determining the occurrence of a switch failure.
For a better understanding of the present invention, together with other and further advantages and features thereof, reference is made to the following description taken in connection with the accompanying drawing, the scope of the invention being pointed out in the appended claims.